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Defining a polynomial viscosity depending on temperature

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Old   September 28, 2020, 04:28
Default Defining a polynomial viscosity depending on temperature
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Muhammed Emin POLAT
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Hello all,

I'm currently trying to run an analysis using temperature integrated simpleFoam. As of my observations, temperature range for the fluid is between 20-50 C and due to this large range, viscosity changes in a wide range which leads my computation into a big error, at about 50%.

So here is my question. I would like to apply a curve-fitting to viscosity of my fluid flowing through and integrate it in the OpenFOAM by NOT using a non-Newtonian approach. Because fluid is definetely Newtonian.

How can I achieve it?
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Old   September 29, 2020, 05:30
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There are more options. Either you switch to, e.g., rhoSimpleFoam and use a polynomial approach or you derive your current solver (simpleFoam) and implement new volScalarFieldīs which relates to temperature and viscosity. Then you have to solve an appropriate temperature/energy equation and calculate the viscosity based on your temperature field.

Probably, the rhoSimpleFoam solver fits better as you donīt have to program anything yourself. An example:

Code:
thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       polynomial;
    thermo          hPolynomialt;
    equationOfState polynomial;
    specie          specie;
    energy          sensibleEnthalpy;
}
The thermo and equation of state polynomials might be just set-up with the first coefficient (its the constant). The transport polynomial is related to the viscosity.
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Old   September 30, 2020, 02:30
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Thank you for your reply Tobi,


The thing is I would like to compute the viscosity for each cell using its temperature and have this value used in governing equations. I don't want any contour for viscosity, to say. Do you have any recommendation for this goal?



Quote:
Originally Posted by Tobi View Post
There are more options. Either you switch to, e.g., rhoSimpleFoam and use a polynomial approach or you derive your current solver (simpleFoam) and implement new volScalarFieldīs which relates to temperature and viscosity. Then you have to solve an appropriate temperature/energy equation and calculate the viscosity based on your temperature field.

Probably, the rhoSimpleFoam solver fits better as you donīt have to program anything yourself. An example:

Code:
thermoType
{
    type            heRhoThermo;
    mixture         pureMixture;
    transport       polynomial;
    thermo          hPolynomialt;
    equationOfState polynomial;
    specie          specie;
    energy          sensibleEnthalpy;
}
The thermo and equation of state polynomials might be just set-up with the first coefficient (its the constant). The transport polynomial is related to the viscosity.
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Old   September 30, 2020, 02:36
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Well, I am not sure if you read my reply or not because I wrote the stuff you need. Hence, I don't get your statement.
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Old   September 30, 2020, 04:06
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Thank you for your help and kindness.
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Old   September 30, 2020, 04:52
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Just a quick question. Is it clear to you now or not? I don't have the feeling that my statement is sufficient for you or maybe I misunderstood your inquiry!?
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